This invention relates to a kinetofrictional force testing apparatus. More particularly, it relates to a kinetofrictional force testing apparatus in which a magnetic disk, for example, is used as a sliding member and relative frictional forces generated between the magnetic disk and a corresponding test head, such as a magnetic head by starting and stopping the rotation of the magnetic disk can be measured with a high sensitivity.
Many magnetic disk devices employed in recent years are operated by the so-called contact start/stop method (CSS method). According to this method, while a magnetic disk is a standstill, it is in contact with a magnetic head. After the magnetic disk has started rotating, the magnetic head gradually rises above the surface of the magnetic disk, and when the magnetic disk has reached a certain predetermined rotating speed (usually 3600 RPM), the magnetic head floats above the surface of the magnetic disk.
Assessments of the durability of the magnetic disk and the magnetic head are made by measuring the relative frictional forces between the magnetic disk and the magnetic head, and a test method therefor is clearly prescribed in ANSI Standards. However, these standards contain no stipulations concerning the frequency response of a load cell sensor. Therefore, various test results can be produced depending upon the frequency responses of the load cell sensors used. The frequency responses of the load cell sensors presently in use are at most 50 Hz, and when the rotational frequency of the magnetic disk is raised, the frequency component of the frictional force shifted to a high frequency side and the resonant frequency component of a measuring system are superposed to render accurate measurement impossible. In the prior art technique of this type, accordingly, the rotational frequency must be set at 10 RPM or below for the purpose of enhancing the accuracy of the measurement.
The durability of a magnetic disk device is governed by kinetic frictional characteristics based on the rise and fall of the rotational speed at the start and stop of the magnetic disk device. It is therefore necessary to precisely measure the kinetic frictional forces in the cases where the rotational frequency changes by several hundred RPM in a short time (usually within 1 second).
A rotational drive system for a conventional magnetic disk device is furnished with individual motors for low speeds and for high speeds, and rotational speeds of, for example, 0.1 RPM through 4000 RPM are covered by properly switching and actuating these motors. With such a rotational drive system, however, a complicated mechanism is necessitated, and a wide range of rotational frequencies cannot be continuously controlled in a short time. In addition, a construction is adopted wherein the load cell sensor used is stopped by stopper means, and the load cell sensor is sensitive in a limited direction. It is therefore impossible to use the sensor to measure both the up and down motions of the magnetic head.